src/main/java/org/apache/xmlbeans/impl/common/XBLogFactory.java

/*   Copyright 2017, 2018 The Apache Software Foundation
 *
 *   Licensed under the Apache License, Version 2.0 (the "License");
 *   you may not use this file except in compliance with the License.
 *   You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *   Unless required by applicable law or agreed to in writing, software
 *   distributed under the License is distributed on an "AS IS" BASIS,
 *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *   See the License for the specific language governing permissions and
 *  limitations under the License.
 */

package org.apache.xmlbeans.impl.common;

import java.util.HashMap;
import java.util.Map;

/**
 * Provides logging without clients having to mess with
 * configuration/initialization.
 *
 * @author Andrew C. Oliver (acoliver at apache dot org)
 * @author Marc Johnson (mjohnson at apache dot org)
 * @author Nicola Ken Barozzi (nicolaken at apache.org)
 */
public final class XBLogFactory {
    /**
     * Map of XBLogger instances, with classes as keys
     */
    private static final Map<String,XBLogger> _loggers = new HashMap<String,XBLogger>();

    /**
     * A common instance of NullLogger, as it does nothing
     *  we only need the one
     */
    private static final XBLogger _nullLogger = new NullLogger();
    /**
     * The name of the class to use. Initialised the
     *  first time we need it
     */
    static String _loggerClassName = null;

    /**
     * Construct a XBLogFactory.
     */
    private XBLogFactory() {}

    /**
     * Get a logger, based on a class name
     *
     * @param theclass the class whose name defines the log
     *
     * @return a XBLogger for the specified class
     */
    public static XBLogger getLogger(final Class<?> theclass) {
        return getLogger(theclass.getName());
    }

    /**
     * Get a logger, based on a String
     *
     * @param cat the String that defines the log
     *
     * @return a XBLogger for the specified class
     */
    public static XBLogger getLogger(final String cat) {
        // If we haven't found out what logger to use yet,
        //  then do so now
        // Don't look it up until we're first asked, so
        //  that our users can set the system property
        //  between class loading and first use
        if(_loggerClassName == null) {
        	try {
        		_loggerClassName = System.getProperty("org.apache.xmlbeans.impl.store.XBLogger");
        	} catch(Exception e) {
                // ignore any exception here
            }

        	// Use the default logger if none specified,
        	//  or none could be fetched
        	if(_loggerClassName == null) {
                _loggerClassName = _nullLogger.getClass().getName();
        	}
        }

        // Short circuit for the null logger, which
        //  ignores all categories
        if(_loggerClassName.equals(_nullLogger.getClass().getName())) {
        	return _nullLogger;
        }


        // Fetch the right logger for them, creating
        //  it if that's required
        XBLogger logger = _loggers.get(cat);
        if (logger == null) {
            try {
                @SuppressWarnings("unchecked")
                Class<? extends XBLogger> loggerClass =
                    (Class<? extends XBLogger>) Class.forName(_loggerClassName);
                logger = loggerClass.getDeclaredConstructor().newInstance();
                logger.initialize(cat);
            } catch(Exception e) {
                // Give up and use the null logger
                logger = _nullLogger;
                _loggerClassName = _nullLogger.getClass().getName();
            }

            // Save for next time
            _loggers.put(cat, logger);
        }
        return logger;
    }
}